EP 1 413 810 A1 discloses an actuating assembly of the generic type for a turbine valve for controlling the gas or steam supply of a turbine or for a process fitting for controlling a process flow in process engineering. Actuating assemblies of this type usually have an actuating drive which is configured as an electric spindle drive in the subject matter of EP 1 413 810 A1. In a gas turbine, an opening cross section of a fitting can be adjusted, for example, by means of an actuating assembly of this type in order to set a gas supply. In an emergency, for example in the event of a power failure or a disruption, the fitting is to be reset automatically, in order to avoid damage to the plant. To this end, the spindle drive in the known solution is assigned a toggle lever mechanism which is locked in a stretched position during regular operation, that is to say with a sufficient power supply, in which stretched position a prestressing spring is stressed. In the event of a power failure, the locking mechanism releases the toggle lever, with the result that it is adjusted via the prestressing spring from its stretched position into its bent position and, in accordance with this adjustment path, the fitting is adjusted back into its predefined basic position, as a rule the closed position.
A toggle lever mechanism of this type requires considerable outlay in terms of device technology and also takes up a relatively large amount of installation space.
In order to eliminate this disadvantage, DE 10 2009 021 668 A1 by the applicant discloses an actuating assembly, in which a fitting is actuated via a regulating drive and a switching fitting which is arranged in series with respect to the former is actuated via a switching drive. The regulating drive is configured with an emergency actuating means which closes the fitting in the case of a power failure. In contrast to the above-described embodiment, said emergency actuating means is not configured by way of a toggle lever mechanism, but rather by way of a spring which acts on the fitting in the closing direction and which is prestressed hydraulically. In the case of emergency actuation, said prestressing pressure is relieved in the direction of low pressure, with the result that the spring closes the regulating fitting in a controlled manner. In a corresponding way, the switching fitting is also closed in the case of a power failure, with the result that damage to the turbine or the process engineering plant is virtually ruled out. In the subject matter of DE 10 2009 021 668 A1, an electrically actuable fitting valve is arranged in a relief path to the low pressure, which fitting valve is prestressed in the direction of its open position via a spring and can be switched over electrically into a position, in which the relief path is shut off. In the case of a power failure, said relief path is then opened correspondingly, with the result that the spring can be relieved.
One requirement of hydraulic actuating assemblies of this type consists in that the emergency functional capability of the actuating assembly is to be tested during operation and as far as possible without impairment of the operation. It is to be determined here whether the emergency actuating means is intact and, in the case of a power failure, can close the process fitting and/or the switching drive.
In the case of a regulating drive, this test is possible with comparatively low outlay, since the emergency functional capability in the sense of a partial lift test can be interrogated by way of suitable actuation of the regulating drive. A partial lift test of this type cannot be realized by way of conventional actuating assemblies in a switching fitting, since the latter can be switched over via the switching drive merely between the open position and the closed position. The test can then not take place during operation of the turbine or the process engineering plant.